Contact pressure adjusting means

ABSTRACT

A multiphase air magnetic circuit breaker of very high continuous current rating is provided with a compact movable contact structure for each phase thereof by having a first plurality of main contacts positioned in a first transverse row adjacent to and in front of a second plurality of main contacts positioned in a second transverse row. These main contacts are symmetrically arranged on each side of the arcing contact arm, and the arms for the first plurality of main contacts are aligned with and extend over the arms for the second plurality of main contacts. First pivot means provides a common mounting pivotally securing the arms for the arcing contact and first plurality of main contacts to the contact bridge. Second pivot means at one end of the arms for the second plurality of main contacts mounts the latter to the contact bridge and auxiliary bridges at the other end of the arms for the second plurality of main contacts cooperate with the contact bridge to establish the open circuit position for the second plurality of main contacts. Engagement of the first and second pluralities of contacts establishes the open circuit position of the former, and engagement between the second pivot and the arcing contact arm establishes the open circuit position of the latter. Individually adjustable biasing springs are provided for each contact of the first plurality of main contacts, and individually adjustable springs are provided for each section of the auxiliary bridge.

United States Patent [1 1 Lucas et al.

CONTACT PRESSURE ADJUSTING MEANS Inventors: John C. Lucas, Cherry Hill,N.J.;

William A. Huggins, Lansdowne, Pa.

Primary Examiner-J. D. Miller Assistant Examiner-Harvey FendelmanAtrorney0strolenk, Faber et al.

[5 7] ABSTRACT A multiphase air magnetic circuit breaker of very highcontinuous current rating is provided with a compact [11] 3,755,638 [4 1Aug, 28, 1973 movable contact structure for each phase thereof by havinga first plurality of main contacts positioned in a first transverse rowadjacent to and in front of a second plurality of main contactspositioned in a second transverse row. These main contacts aresymmetrically arranged on each side of the arcing contact arm, and thearms for the first plurality of main contacts are aligned with andextend over the arms for the second plurality of main contacts. Firstpivot means provides a common mounting pivotally securing the arms forthe arcing contact and first plurality of main contacts to the contactbridge. Second pivot means at one end of the arms for the secondplurality of main contacts mounts the latter to the contact bridge andauxiliary bridges at the other end of the arms for the second pluralityof main contacts cooperate with the contact bridge to establish the opencircuit position for the second plurality of main contacts. Engagementof the first and second plu ralities of contacts establishes the opencircuit position of the former, and engagement between the second pivotand the arcing contact arm establishes the open circuit position of thelatter. Individually adjustable biasing springs are provided for eachcontact of the first plurality of main contacts, and individuallyadjustable springs are provided for each section of the auxiliarybridge.

12 Claims, 12 Drawing Figures PATENTEUAUG 28 I973 SHEET 1 BF 7 CONTACTPRESSURE ADJUSTING MEANS This invention relates to molded case circuitbreakers in general and more particularly relates to adjustable contactpressure means for the compact movable contact structure of a moldedcase circuit breaker having a high continuous current rating.

The separable contact structure of any circuit breaker must be capableof carrying the rated current of the circuit breaker continuouslywithout overheating and must be able to withstand arcing that occursbetween the separable contacts during interruption of overload currentswithin the interruption rating of the circuit breaker.

Prior art molded case circuit breakers of lower ratings have, for themost part, one pair of separable contacts per phase to carry out thefunctions of continuously carrying the rated current of the breaker andwithstanding arcing during overload. In some constructions thestationary contact is modified for operation in conjunction with an arcrunner, and the moving contact is provided with an extension or are hornto facilitate arch interruption during high overloads. On moderatelyhigh-rated molded case circuit breakers, separate pairs of contacts arecommonly provided for each of the aforesaid functions, with one pair ofarcing contacts per phase also commonly being provided. A single pair ofarcing contacts'for each phase is usually sufficient when used inconjunction with one or more pairs of main contacts that are used tocarry the rated current continuously.

- In the usual contact configuration for a molded case circuit breakerhaving more than one pair of main contacts, the pain of arcing contactsusually extends forward of the main contacts and into the arcinterrupter and-the main contact pairs are arranged in a single row tothe rear of the arc interrupter, as illustrated in U. S. Pat. Nos.3,198,924 and 3,268,702. An increase in the continuous current rating ofthe circuit breaker brings with it a requirement that a number of maincontact pairs required is increased, so that. it may become necessary toincrease the width of each pole considerably in order to accommodate allcontact pairs of that pole unit in a single row transverse to the planeof movement of the movable contact structure. For many molded casecircuit breaker constructions, the length of the movable contact row isthe factor limiting minimum width of the circuit breaker.

In order to maintain at a minimum the overall width of a molded casecircuit breaker having a very high continuous current rating, usually atleast 2,000 amperes at 600 volts, the instant invention arranges themain contacts of each phase into two parallel rowspositioned one behindthe other and transverse to the plane of movement for the contactstructure. This contact arrangement achieves considerable saving ofspace so that the resulting circuit breaker is not excessively wide.Utilizing a novel arrangement of a contact bridge and auxiliary bridges,the contacts are mounted to the contact bridge in a configuration thatprovides the requisite number of contact adjusting points andestablishes the proper sequencing of the arcing and main contacts duringopening and closing of the circuit breaker.

Accordingly, a primary object of the instant invention is to provide acompact movable contact structure for a very high current molded casecircuit breaker.

Another object is to provide each phase. of a molded case circuitbreaker with a plurality of movable contacts arranged in first andsecond rows behind the arcing contacts, with a requisite number ofcontact pressure adjusting points.

Still another object is to provide a contact structure of this type inwhich sequencing between arcing and main contacts is achieved in asimplified manner.

These objects as well as other objects of this invention will becomereadily apparent after reading the following description of theaccompanying drawings in which:

FIG. 1 is a plan view of a circuit breaker constructed in accordancewith teachings of the instant invention.

FIG. 2 is a longitudinal cross-section taken through line 22 of FIG. 1,looking in the direction of arrow 2-2 and including a handle operatingmechanism, not shown in FIG. 1.

FIG. 3 is an exploded perspective of one overcenter toggle mechanism andselected elements connected thereto.

FIG. 4 is an exploded perspective of the movable contact structure forone phase.

FIG. 5 is a plan view of the movable contact structure and itsovercenter toggle operating mechanism for the center phase of thecircuit breaker of FIG. 1.

FIG. 6 is a side elevation of the elements of FIG. 5, looking in thedirection of arrows 6-6 of FIG. 5.

FIG. 7 is a cross-section taken through line 77 of FIG. 5, looking inthe direction of arrows 77.

FIGS. 8 and 9 are cross-sections taken through the respective lines 88and 9-9 of FIG. 6, looking in the directions of the respective pairs ofarrows 8-8 and 9--9.

FIG. 10 is a fragmentary plan view similar to that of FIG. 5, with mostof the overcenter toggle operating mechanism removed.

FIGS. 11 and 12 are cross-sections taken through line lI-ll of FIG. 10,looking in the direction of arrows l l--1l. In FIG. 11 the contactmechanism is in its open position, and in FIG. 12 the contact mechanismis in its closed position.

Now referring to the figures. Three phase molded case circuit breaker 25of FIGS. 1 and 2 includes an individual overcenter spring-powered toggleoperating mechanism. Prior art examples of circuit breakers having morethan a single operating mechanism for all phases are disclosed in U. S.Pat. Nos. 2,067,935 and 3,125,653.

Circuit breaker 25 includes a molded housing constructed of base 26 andremovable cover 27 joined along line 28 and provided with longitudinalinternal partitions 31, 32 which divide housing 26, 27 into threelongitudinally extending compartments, one for each phase of circuitbreaker 25. Cover 27 is provided with aperture 29 through which stubbybifurcated extension 33 of operating handle means 30 extends. Eachsection of handle extension 33 receives an individual pin 34 extendingupwardly from the web portion of inverted generally U-shaped operatingyoke member 35 of the center phase. Operating members 35 of the outerphases are each secured to handle means 30 by a pair of screws 152.

Member 35 is pivoted to the spaced arms of generally operating mechanismframe 36 at outwardly extending lugs 37. Bolts 48, received by threadedapertures of intumed edges 36a at the bottom of frame 36, fixedly securethe latter to base 26. Transverse tie member 49 is riveted to the armsof frame 36 to maintain spacing therebetween and to stabilize the framestructure.

Four-tensioned coil springs 38, each connected at one end thereof to theweb of operating member 35, combine to constitute the main operatingspring means for the overcenter toggle-type contact operating mechanism.The other ends of springs 38 are connected to spaced plates 39, 39 thatare pivotally mounted to toggle knee pin 4] connecting upper 42 andlower 43 toggle links. The upper ends of upper toggle links 42 arepivotally connected to the spaced arms of latchable cradle 40 at pins44, and the lower ends of lower toggle links 43 are pivotally connectedto contact carrier 45 by rod 46 that extends between the spaced arms ofcontact carrier 45. The spaced arms of cradle 40 are positioned adjacentthe inner surfaces of the spaced arms of frame 36 and are pivotallyconnected thereto by pins 47 that are secured to frame 36.

Under normal operating conditions plate 51, secured to web 40a of cradle40, is in engagement with forward latching surface 52 of auxiliary latch53. The latter is loosely mounted to pivot rod 55 extending between thespaced arm of mechanism frame 36 and slightly outboard thereof. Thecoiled end sections of torsion spring member 56 are wound about pivotrod 55, with the ends of these sections bearing against rod 57 andauxiliary latch 53 to bias the latter counterclockwise against stop rod58. The ends of rods 57 and 58 are supported by the arms of frame 36.Leaf spring 73 secured to auxiliary latch 53 bears against pivot rod 55biasing latch 53, so that rod 55 will normally lie at the centralportion of V-shaped notch 74 of primary latch 53.

The ends of rod 55 projecting outboard of mechanism frame 36 are engagedby the hooked portions at the forward extensions 59 of the arms forU-shaped trip unit frame 60, whose web portion is seated on a forwardsurface of load strap 61, being secured thereto by bolts 62 that extendthrough clearance apertures in strap 61 and are received by threadedinserts molded in base 26.

Rear latch tip 54-engages latch tip 63. at the U-qhaped forward arm ofprimary latch 65, whose rear latch tip 64 is engaged by latch plate 67mounted on one leg of L-shaped carrier 66. Primary latch 65 is pivotallymounted to trip unit frame 60 at stub shaft 69, and the carrier ispivoted on rod 68 to frame 60. Tension spring 75 biases primary latch 65in a clockwise direction about pivot 69. The other leg of carrier 66 isprovided with transversely extending pin 71 that projects intotriangular window 72 of primary latch 65 at a portion thereof near rearlatch tip 64, for a reason to be hereinafter explained. Tension spring76, connected between frame 60 and carrier extension 66a, biases carrier66 in a counterclockwise direction about its pivot 68 toward latchingposition.

When automatic tripping occurs, carrier 66 in the faulted phase is movedclockwise either by the deflection of bimetal 77 or movement of magneticarmature 78, causing latch plate 67 to release primary latch 65, whichin turn releases secondary latch 53 and permits main operating springs38 to rotate cradle 40 in a counterclockwise direction to break toggle42, 43. The force from main spring 38 acts through cradle 40, primarylatch 53, and secondary latch 65 to drive cam surface 78, boundingopening 72, against extension 71 to rotate carrier 66 clockwise, withsurface 79 thereof engaging ear 81 of extension 82 on tripper bar 80which extends between all threephases. This causes tripper bar 80 torotate in a counterclockwise direction, so that extensions 82 in thenon-faulted phases rotate counterclockwise with cam surfaces 83 thereofengaging transversely extending pin 84 of carriers 66 in the nonfaultedphases rotating them clockwise or in the tripping direction, to releasethe cradle latching system in the non-faulted phases, so that thecontacts of all three phases are open.

In order to prevent closing of the contacts of any one phase before theoperating mechanisms of all phases are latched, circuit breaker 25 isprovided with a defeater latching system including defeater latch 80'and defeater lever 90. Latch 80 is pivotally mounted upon rod 55 andincludes protrusion 81 extending over the rear of cradle when the latteris in latched position. Latch 80' further includes protrusion 82'extending over the forward end of defeater lever 90 in slot 91 thereof.Coiled tension spring 83' is connected between stop rod 57 and latch80', passing partially around rod 55, to bias latch 80 in acounterclockwise direction about its pivot 55 and maintaining this pivotin the basic position at the right end of slot 84' in latch 80'. Thisbasic position is established through the engagement of latch stopsurface 86 and stop rod 57.

Slot 91 is in the web of the U-shaped forward portion of latch lever 90,with the U arms having pivot pin 69 for lever 90 extending therethrough.Rear portion 89 of lever 90 is positioned below and in interferingrelationship with transverse pin 71 mounted to latch plate carrier 66.

During normal relatching of circuit breaker 25, inwardly protrudingportions of the operating member 35 arms engage outboard portions of pin44 to pivot cradle 40 clockwise, whereby the latter cams defeater latch80' away and moves below auxiliary latch 53. Upon re lease of thecircuit breaker operating handle 30, the elements of the latch train 53,65, 66 move into place. However, should any of these elements fail toproperly engage or should cradle 40 not have been moved far enough toengage auxiliary latch 53, cradle 40 will pick up defeater latchprotrusion 81', causing clockwise rotation of defeater latch In turn,this causes defeater latch protrusion 82' to engage defeater lever androtate the latter counterclockwise, with the rear end 89 thereofcontacting carrier extension 71 so that latch plate carrier 66 ispivoted in a clockwise or latch train releasing direction. During thisreleasing movement of carrier 66, surface 79 thereof engages nose 81 ofone trip bar extension 82 to rotate common tripper bar 80 in acounterclockwise direction, with the other extensions 82 on bar 80engaging pins 84 on the latch pole carriers 66 of the other poles,thereby causing the latch systems of all other poles to be released.

The lower end of bimetal 77 is fixedly secured to shading coil 99, andthese elements are fixedly secured to molded frame member secured totrip unit frame 60. The horizontal leg of inverter U-shaped stationarymagnetic frame member 98 passes through the center of coil 99. Member 98is secured to the rear of frame 60, with the vertical legs of member 98being on opposite sides of load strap 61. The other U-shaped magneticframe member 96 is secured directly to load strap 61, with the ends ofthe arms for frame members 96 and 98 confronting one another in spacedrelationship. Thus, current flowing in load strap 61 generates flux inmagnetic frame 96, 98 which induces current flow in shading coil 99 andthereby generates heat that is conducted to bimetal 77 for heatingthereof. Coiled tension spring 97, connected between armature 78 and anelement mounted to the rear transverse part 60a of frame 60, biases theformer away from two spaced legs 98a extending upward from thehorizontal leg of member 98 and is drawn downward toward legs 98a whenoverload currents generate sufficient magnetic flux in magnetic frame78, 96, 98.

With particular reference to FIG. 4, it is seen that the movable contactstructure for each phase of circuit breaker 25 includes eight maincontacts 103-110 and a single arcing contact 101. The latter contact 101is mounted at the forward end of arm 112, which is pivotally mounted tocarrier 45 at toggle connecting rod 46. Main contacts 103-110 arearranged in two parallel rows positioned to the rear of arcing contact101 and disposed at right angles to the plane of movement of arcingcontact arm 112.

Main contacts 103-106 in the forward row are mounted to individualcontact arms 113-116 respectively, all pivotally mounted to carrier 45on rod 46. Main contacts 107-110 in the rear row are mounted to theforward end of the respective contact arms 117-120, respectively,pivotally mounted to carrier 45 on rod 102. All of the contact arms112-120 are connected to load strap 61 by means of individual stacks 121of flexible sheet conductors. Contact arms 113-116 are in alignment withand extend over the respective contact arms 117-120, so that the lattergroup of arms 117-120 block downward movement of the former group ofarms 113-116 to establish the open circuit position of contacts 103-106in a manner which will hereinafter be seen. The open circuit positionfor arcing contact arm 112 is established through engagement thereofwith aligned pins 123, 124 which mount the respective pairs of maincontacts 117, 118 and 119, 120 to auxiliary carriers 125, 126respectively. Notch 122 along the lower edge of arcing contact arm 112provides clearance for pins 123, 124.

Auxiliary carrier 125 is an inverted U-Shaped member whose arms extenddownwardly through cutouts 131, 132 in the web portion of contactcarrier 45 and straddle four contact arms 113, 114, 117, 118. Pin 123secur'es contacts 117, 118 to the lower ends of the arms comprisingauxiliary carrier 125. The web of auxiliary carrier 125 is biasedtowards the web of contact carrier 45 by coiled compression spring 127,which is wound around the threaded body of bolt 128 whose head ispositioned below the web portions of contact carrier 45. Self-lockingnut 133 mounted to bolt 128 is rotated to adjust the loading of spring127, with the rectangular shoulder of bolt 128 cooperating withrectangular cutout in carrier 45 to prevent rotation of bolt 128. Thusit is seen that in the open circuit position of FIG. 11, spring 127biases the web of auxiliary contact carrier 125 against the web ofcontact carrier 45, and as seen in FIG. 12, when the contacts are closedthere is a space between the webs of these contact carriers 45, 125, sothat the force exerted by spring 127 acts to bias contacts 107, 108 intofirm electrical engagement with their respective cooperating contactportions on line strap 136.

The mounting of contact arms 119, 120 to auxiliary contact carrier 126and mounting of the latter to contact carrier 45 is the same as themounting of contact arms 117, 118 and auxiliary carrier 125, so thatthis description will not be repeated.

Biasing forces for each of the contacts 103-106 in the forward row areprovided by individual coiled compression springs 138, and each of thesesprings is mounted in the same way so that only the mounting of one ofthese springs will be described. The lower end of spring 138 extendsinto depression 139 in the upper surface of main contact arm 113, andthe rear of spring 138 extends into tubular support 141 through the openbottom thereof. Support 141 is mounted to the upper surface of carrierat the web portion thereof, and its upper end is threaded to receiveadjusting screw 142 whose lower end bears against disc 143 abutting theupper end of spring 138. If screw 142 is adjusted to set the contactpressure exerted by spring 138, lock nut 144 is tightened to lock thisadjustment.

in order to increase the area of engagement between main contacts103-110 and their respective cooperating stationary main contacts in thevery limited space available, it is noted that each of the main contactsis provided with a portion extending outward of its respective contactarm. That is, in order to utilize the space below arcing contact 112,main contacts 104, 105, 108, 109 have been extended beyond theirrespective contact arms 114, 115, 118, 119 to project below arcingcontact arm 112. Similarly, main contacts 103, 106, 107, 110 have beenextended outboard from their respective contact arms 113, 116, 117, 120,to lie in the space below the outboard arms of auxiliary contact carrier125, 126 and other elements used to connect the movable contactstructure to the contact operating mechanism.

The forward end of arcing contact arm 112 is biased downward away fromthe web portion of contact carrier 45 by coiled compression spring 171whose lower end is positioned by pin 172 extending upward from arm 112.The upper end of spring 171 extends into tubular member 173, on theupper surface of the carrier 45 web portion, through the bottom ofmember 173 and abuts the closed upper end thereof.

The spaced arms of contact carrier 45 are provided with rearwardextensions 45a, 45b that are spaced by and secured to shoulderedcylindrical tube 146. After all contact structures, operatingmechanisms, latching devices, and automatic trip units are mounted tobase 26, and all adjustments to these mechanisms have been made, thecontact structures of all phases are operated to the closed circuitposition, so that the tubular mem bers 146 of all phases are axiallyaligned and'are positioned above barriers 31, 32 and the longitudinalsides of base 26. Thereafter, cylindrical tie bar 147 is drivenlongitudinally in the members 146 of all phases to constitute a rigidmechanical connection between the movable contact structures of allphases. The fit between tie rod 147 and tubular members 146 is tightenough to prevent unintentional axial movement of tie rod 147,

yet permits tie rod 147 to be removed for convenient servicing andreplacement of parts. Mechanism frame 36 is provided with alignedelongated slots 148 to provide clearances for movement ofrod 147 duringopening and closing of the movable contact structures.

It is noted that because of high magnitude current flow in circuitbreaker 25, the magnetic fields generated are very strong.- In order toreduce adverse effects of these magnetic fields, many of the frame partsand operating mechanism parts are constructed of nonmagnetic stainlesssteel.

For those features of construction in circuit breaker 25 that have notbeen described in detail herein, reference is made to one or more of thecopending applications Ser. Nos. 275,568, 275,577, 275,578, 275,507,275,454, 275,508, 275,261, 275,623, 275,624, 275,569, 275,522, 275,521,275,523, and 275,622, all filed of even date herewith, and all assignedto the assignee of the instant invention.

Although there has been described a preferred embodiment of this novelinvention, many variations and modifications will now become apparent tothose skilled in the art. Therefore, this invention is to be limited notby the specific disclosure herein but only by the appending claims.

The embodiments of the invention in which an exclusive privilege orproperty is claimed are defined as follows.

l. A circuit breaker including cooperating contact means for a polethereof; said cooperating contact means including relatively stationarycontact means and relatively movable contact means movable in a plane ofmovement between open and closed circuit positions wherein said movablecontact means is respectively disengaged from and engaged with saidstationary contact means; an operating means for moving said movablecontact means between its said open and closed circuit positions; saidmovable contact means including an arcing contact, a first plurality ofmain contacts arranged generally in a first row perpendicular to saidplane and behind said arcing contact, and a second plurality of contactsarranged generally in a second row perpendicular to said plane; saidsecond row being adjacent to and behind said first row; said stationarycontact means being below said movable contact means; a plurality ofmovable arms each having one of said main contacts mounted thereto atits forward end; said arms for said first plurality of main contactsextending rearward therefrom and above the arms for said secondplurality of main contacts; a main bridge interposed between saidoperating means and said movable contact means; a first pivot meansmounting said arms for said first plurality of main contacts to saidbridge; a second pivot means parallel to and laterally offset from saidfirst pivot means; said second pivot means mounting said arms for saidsecond plurality of main contacts to said bridge; first biasing meanssupported by said bridge and urging said first plurality of maincontacts toward said stationary contact means; auxiliary bridge meansconnected to said arms for said second plurality of main contacts at aposition forward of said second pivot means; second biasing meanssupported by said bridge and acting through said auxiliary bridge meansto urge said second plurality of main contacts toward said stationarycontact means.

2. A circuit breaker as set forth in claim 1 in which, with therelatively movable contact means in its said open circuit position,engagement between said bridge and said auxiliary bridges establishesthe position of said second plurality of main contacts relative to saidbridge and engagement between the arms for said first plurality of maincontacts and the arms for said second plurality of main contactsestablishes the position of said first plurality of main contactsrelative to said bridge.

3. A circuit breaker as set forth in claim 2 in which the first biasingmeans comprises a first set of springs each acting directly on anindividual one of the arms for the first plurality of main contacts; andadjusting means for individual adjustment of the forces exerted by eachof said springs.

' 4. A circuit breaker as set forth in claim 3 in which the bridgecomprises an inverted generally U-shaped portion having spaced armsconnected by a web and the auxiliary bridge comprises an invertedgenerally U- shaped member having spaced arms connected by a web; saidarms of said auxiliary bridge positioned between the arms of said bridgeand said web of said auxiliary bridge positioned above the web of saidbridge; said second biasing means including a spring acting directly onsaid auxiliary bridge and additional means for adjusting the forceexerted by said second biasing means.

5. A circuit breaker as set forth in claim 4 in which the adjustingmeans and the additional adjusting means are both accessible foroperation from above said bridge.

6. A circuit breaker as set forth in claim 5 in which there is athreaded member extending upward from said bridge and through saidauxiliary bridge; said spring of said second biasing means being acoiled member through which said threaded member extends; saidadditional means bearing against the upper end of said spring of saidsecond biasing means and being in threaded engagement with said threadmember.

7. A circuit breaker as set forth in claim 1 in which the auxiliarybridge comprises first and second inverted generally U-shaped memberseach having spaced arms connected by a web; a first and a second of saidarms for contacts of said second plurality of main contacts beingpositioned between and pivotally secured to said arms of said auxiliarybridge; a third and a fourth of said second plurality of main contactsbeing positioned between and pivotally secured to said arms.

8. A circuit breaker as set forth in claim 7 in which the numbers ofmain contacts in said first and second rows are equal.

9. A circuit breaker as set forth in claim 7 in which the bridgeincludes a generally U-shaped member having a web connected by spacedarms; said webs of both of said first and second U-shaped memberspositioned above the web of the bridge.

10. A circuit breaker as set forth in claim 9 in which the first biasingmeans comprises a first set of springs each acting directly on anindividual one of the arms for the first plurality of main contacts; andadjusting means for individual adjustment of the forces exerted by eachof said springs; said second biasing means including an individualspring for each of said auxiliary bridges; additional adjusting meansfor each spring of said additional biasing means for adjusting theforces exerted by said springs of said additional means.

. 11. A circuit breaker as set forth in claim 1 in which there is an armhaving said arcing contact at one end thereof; biasing means urging saidarcing contact toward said stationary contact means; said arm of saidarcing contact being mounted near its other end to said first pivotmeans; means connected with the arms of said second plurality of maincontacts and operatively positioned to engage the arm of said arcingcontact and thereby establish the position thereof relative to saidbridge when said relatively movable contact means is in its said opencircuit position.

12. A circuit breaker as set forth in claim 11 in which, with therelatively movable contact means in its said open circuit position,engagement between said bridge and said auxiliary bridges establishesthe position of said second plurality of main contacts relative

1. A circuit breaker including cooperating contact means for a polethereof; said cooperating contact means including relatively stationarycontact means and relatively movable contact means movable in a plane ofmovement between open and closed circuit positions wherein said movablecontact means is respEctively disengaged from and engaged with saidstationary contact means; an operating means for moving said movablecontact means between its said open and closed circuit positions; saidmovable contact means including an arcing contact, a first plurality ofmain contacts arranged generally in a first row perpendicular to saidplane and behind said arcing contact, and a second plurality of contactsarranged generally in a second row perpendicular to said plane; saidsecond row being adjacent to and behind said first row; said stationarycontact means being below said movable contact means; a plurality ofmovable arms each having one of said main contacts mounted thereto atits forward end; said arms for said first plurality of main contactsextending rearward therefrom and above the arms for said secondplurality of main contacts; a main bridge interposed between saidoperating means and said movable contact means; a first pivot meansmounting said arms for said first plurality of main contacts to saidbridge; a second pivot means parallel to and laterally offset from saidfirst pivot means; said second pivot means mounting said arms for saidsecond plurality of main contacts to said bridge; first biasing meanssupported by said bridge and urging said first plurality of maincontacts toward said stationary contact means; auxiliary bridge meansconnected to said arms for said second plurality of main contacts at aposition forward of said second pivot means; second biasing meanssupported by said bridge and acting through said auxiliary bridge meansto urge said second plurality of main contacts toward said stationarycontact means.
 2. A circuit breaker as set forth in claim 1 in which,with the relatively movable contact means in its said open circuitposition, engagement between said bridge and said auxiliary bridgesestablishes the position of said second plurality of main contactsrelative to said bridge and engagement between the arms for said firstplurality of main contacts and the arms for said second plurality ofmain contacts establishes the position of said first plurality of maincontacts relative to said bridge.
 3. A circuit breaker as set forth inclaim 2 in which the first biasing means comprises a first set ofsprings each acting directly on an individual one of the arms for thefirst plurality of main contacts; and adjusting means for individualadjustment of the forces exerted by each of said springs.
 4. A circuitbreaker as set forth in claim 3 in which the bridge comprises aninverted generally U-shaped portion having spaced arms connected by aweb and the auxiliary bridge comprises an inverted generally U-shapedmember having spaced arms connected by a web; said arms of saidauxiliary bridge positioned between the arms of said bridge and said webof said auxiliary bridge positioned above the web of said bridge; saidsecond biasing means including a spring acting directly on saidauxiliary bridge and additional means for adjusting the force exerted bysaid second biasing means.
 5. A circuit breaker as set forth in claim 4in which the adjusting means and the additional adjusting means are bothaccessible for operation from above said bridge.
 6. A circuit breaker asset forth in claim 5 in which there is a threaded member extendingupward from said bridge and through said auxiliary bridge; said springof said second biasing means being a coiled member through which saidthreaded member extends; said additional means bearing against the upperend of said spring of said second biasing means and being in threadedengagement with said thread member.
 7. A circuit breaker as set forth inclaim 1 in which the auxiliary bridge comprises first and secondinverted generally U-shaped members each having spaced arms connected bya web; a first and a second of said arms for contacts of said secondplurality of main contacts being positioned between and pivotallysecured to said arms of said auxiliary bridge; a third and a fourth ofsaid second plurality of main contacts being positioned between andpivotally secured to said arms.
 8. A circuit breaker as set forth inclaim 7 in which the numbers of main contacts in said first and secondrows are equal.
 9. A circuit breaker as set forth in claim 7 in whichthe bridge includes a generally U-shaped member having a web connectedby spaced arms; said webs of both of said first and second U-shapedmembers positioned above the web of the bridge.
 10. A circuit breaker asset forth in claim 9 in which the first biasing means comprises a firstset of springs each acting directly on an individual one of the arms forthe first plurality of main contacts; and adjusting means for individualadjustment of the forces exerted by each of said springs; said secondbiasing means including an individual spring for each of said auxiliarybridges; additional adjusting means for each spring of said additionalbiasing means for adjusting the forces exerted by said springs of saidadditional means.
 11. A circuit breaker as set forth in claim 1 in whichthere is an arm having said arcing contact at one end thereof; biasingmeans urging said arcing contact toward said stationary contact means;said arm of said arcing contact being mounted near its other end to saidfirst pivot means; means connected with the arms of said secondplurality of main contacts and operatively positioned to engage the armof said arcing contact and thereby establish the position thereofrelative to said bridge when said relatively movable contact means is inits said open circuit position.
 12. A circuit breaker as set forth inclaim 11 in which, with the relatively movable contact means in its saidopen circuit position, engagement between said bridge and said auxiliarybridges establishes the position of said second plurality of maincontacts relative to said bridge and engagement between the arms forsaid first plurality of main contacts and the arms for said secondplurality of main contacts establishes the position of said firstplurality of main contacts relative to said bridge.